Optical module

ABSTRACT

An optical module which can be made more compact and lightweight. An end portion ( 18 ) of a mounting substrate ( 10 ) forms a mirror which reflects light through 90 degrees. A surface-emission laser ( 22 ) is disposed so that a light-emitting aperture ( 28 ) faces the end portion ( 18 ). Within the mounting substrate ( 10 ) are formed a core ( 12 ) extending along the plane of the mounting substrate ( 10 ) and a cladding ( 14 ). The mounting substrate ( 10 ) doubles as an optical waveguide. Therefore, the optical module can be made thinner. As a result, the optical module can be made more compact and lightweight.

TECHNICAL FIELD

The present invention relates to an optical module which is formed byintegrating an optical element, optical waveguide, or the like.

BACKGROUND ART

An optical module is a transducer from electrical energy to light, orfrom light to electrical energy. An optical module is constituted inhybrid integrated form by an optical element, an optical waveguide, anelectrical circuit, and the like. An optical module is used, forexample, in an optical fiber communications system.

FIG. 3 shows schematically the disposition of an optical waveguide andoptical element in a conventional optical module. This is disclosed inthe journal Optical Technology Contact Vol. 36, No. 4 (1998). On aprincipal surface of a mounting substrate 40, a depression 42 isprovided. In the depression 42 is mounted an optical element 44. On theprincipal surface of the mounting substrate 40 is fitted an opticalwaveguide 46. The end portion 48 of the optical waveguide 46 ispositioned over the optical element 44. The end portion 48 forms amirror. Light 50 emitted by the optical element 44 is reflected by theend portion 48, and enters the core 52 of the optical waveguide 46. Thelight 50 proceeds in the direction shown by an arrow within the core 52,and is transmitted through the optical fiber or the like.

However, this requires both alignment accuracy when mounting the opticalelement on the mounting substrate and alignment accuracy between themounting substrate on which the optical element is mounted and theoptical waveguide. In particular, for an optical module such as anoptical fiber requiring positioning accuracy with an error of ±1 to ±5μm, there is also a requirement to reduce as far as possible the numberof locations at which this alignment accuracy is required.

Further, electronic instruments are required to be more compact andlightweight, as a result of which, compactness, light weight, and lowcost are requirements for optical modules.

This invention solves this problem. The objective of this invention isthe provision of an optical module which can be made more compact andlightweight.

DISCLOSURE OF THE INVENTION

(1) An optical module of this invention comprises:

a mounting member having a principal surface; an interconnect formed onthe mounting member; and an optical element mounted on the principalsurface and electrically connected to the interconnect,

wherein the mounting member is an optical waveguide for guiding lightemitted from the optical element or light admitted to the opticalelement.

In a conventional optical module, on a mounting member is mounted anoptical waveguide separate from the mounting member. Incontradistinction, this invention has the mounting member and opticalwaveguide as an integral member. The optical module can therefore bemade thinner. As a result, the optical module can be made more compactand lightweight.

In a conventional optical module, there are three members involved inthe positioning: the mounting member, the optical waveguide, and theoptical element. On the other hand, in this invention there are two: themounting member (optical waveguide) and the optical element. Therefore,in this invention, the optical element positioning is made easier, andthe bonding accuracy can be improved.

A light-admitting aperture or light-emitting aperture of the opticalelement may be disposed opposing the principal surface. Such an opticalelement may be, for example, a surface-emission laser.

A light-reflecting member may be provided on the optical waveguide.Through the light-reflecting member, light can be transmitted betweenthe optical element and the optical waveguide.

(2) An optical module of this invention comprises: an optical elementfor emitting or admitting light; and an optical waveguide having aprincipal surface, with the optical element mounted on the principalsurface, for guiding light emitted from the optical element or lightadmitted to the optical element.

This aspect of the invention has the same effect as the aspect (1) ofthe invention.

The optical element and the optical waveguide may be fixed with anadhesive member having light transmitting characteristics interposedbetween the optical element and the optical waveguide in such a way thatthe position of emission or admission of light of the optical elementopposes the optical waveguide, and be subjected to bare chip mounting.

Bare chip mounting allows more compact and lightweight design than withpackage mounting. In this aspect, since the optical element is subjectedto bare chip mounting, the optical module can be made more compact andlightweight. The optical element and optical waveguide and are fixed byan adhesive member having light transmitting characteristics. By virtueof this, the optical element and the optical waveguide can be fixed andan optical path between the optical element and the optical waveguidecan be assured.

The optical waveguide may have a modifying portion whereby the directionof progress of the light is changed; and the optical element may bepositioned to overlie the modifying portion. By virtue of this, thedirection of progress of the light can be efficiently changed.

The modifying portion is formed in the optical waveguide, and theoptical element is directly mounted to the optical waveguide having themodifying portion. By virtue of this, the relative positioning (distanceand the like) of the optical element and modifying portion can always bemaintained constant, as a result of which there can be no loss of focuswith respect to the modifying portion. On the other hand, in the priorart, the optical element is not mounted directly on the opticalwaveguide, and therefore the optical waveguide and optical element aredisposed separated from each other. For this reason, when both are fixedwith respect to other elements, there is a possibility of relativemovement between the two. Therefore, even if the positioning operationis achieved, thereafter there is the possibility of a change in thepositioning caused by various influences (heat, external pressure, andthe like).

It should be noted that in the expression “positioned to overlie themodifying portion,” the term “overlie” indicates that when seenprojected from the optical element or modifying portion, both aredisposed in positions such that it appears that both coincide.

On the principal surface of the optical waveguide may be further mounteda semiconductor element in addition to the optical element, and theoptical element and the semiconductor element may be integrally sealedwith a resin.

If the optical element and semiconductor element are mounted on theprincipal surface of the optical waveguide, the interconnect connectingthe two may be made shorted. The formation of the interconnect on themounting substrate can be single layer, and the interconnect formationis made easier. If the optical element and semiconductor element areintegrally sealed with a resin, the strength of the optical module canbe improved. If the optical element and semiconductor element arehybrid, the degree of integration of the optical module can be improved.By the improvement of this degree of integration, the cost can belowered.

The resin may have light blocking characteristics. If light impinges onthe semiconductor element, faulty operation of the semiconductor elementis possible. By sealing the semiconductor element with a resin havinglight blocking characteristics, faulty operation can be prevented.

The semiconductor element may have a function of driving the opticalelement.

Since the optical element and the semiconductor element driving orcontrolling the optical element are mounted on the principal surface ofthe optical waveguide, the optical module can be made a module of highadded value. A higher degree of integration of the optical module and alower cost can also be achieved.

A circuit may be laminated directly on the principal surface of theoptical waveguide. If a circuit is laminated directly on the principalsurface of the optical waveguide, the mounting of the semiconductorelement is not required. Therefore, it is no longer necessary toconsider the reliability of connection between different components. Inrespect of connections between integrated circuit elements, theconnections can be eliminated, and by virtue of this, the interconnectimpedance characteristics and noise characteristics can be improved,while the effect of delays can be held to a minimum. The degree ofintegration on the principal surface of the optical waveguide can beimproved, and a high degree of integration of the optical module and lowcost can be achieved.

(3) An optical module of the invention comprises: an optical element;and a mounting member which has a function of an optical waveguide forguiding light emitted from the optical element or light admitted to theoptical element and is electrically connected to the optical element ora semiconductor element associated therewith.

This aspect of the invention has the same effect as the aspect (1) ofthe invention.

(4) An optical module of this invention comprises: a mounting memberhaving a principal surface and a lateral surface; and an optical elementmounted on the principal surface, wherein the mounting member has afunction of an optical waveguide, and an optical input/output terminalfor the optical waveguide is provided on the lateral surface of themounting member.

This aspect of the invention has the same effect as the aspect (1) ofthe invention. It should be noted that an optical input/output terminalmeans a terminal at which light is input, or a terminal at which lightis output, or a terminal at which light is input and/or output.

It should be noted that optical elements include both elements whichemit light and elements which receive light. The mounting member may bein plate, film, or other form, as long as it allows the optical elementto be mounted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross-section of one embodiment of the opticalmodule of this invention;

FIG. 2 shows a schematic plan view of one embodiment of the opticalmodule of this invention; and

FIG. 3 shows schematically the relative disposition of the opticalwaveguide and optical element of a conventional optical module.

BEST MODE FOR CARRYING OUT THE INVENTION Structure

FIG. 1 shows a schematic cross-section of one embodiment of the opticalmodule of this invention. FIG. 2 shows a schematic plan view thereof. Aglass mounting substrate 10 doubles as an optical waveguide. Thus,within the mounting substrate 10 are formed a core 12 and cladding 14extending along the surface for mounting an optical element on themounting substrate 10. The core 12 and cladding 14 are formed within themounting substrate 10 by using thin-film formation techniques,photolithography, or the like.

One end portion 18 of the optical waveguide forms a 45-degree mirror bywhich the light is bent through 90 degrees. The 45-degree mirror isformed by using for example a 90-degree V-shape diamond saw, to machinethe end portion 18 of the optical waveguide. On the lateral surface ofthe mounting substrate 10, and at the other end portion of the opticalwaveguide, is disposed an optical output terminal 29. Light passes alongthe core 12, and is output from the optical output terminal 29.

On the mounting substrate 10, interconnects 16 a, 16 b, and 16 c areformed from a metal foil or the like. In this embodiment, theinterconnects 16 a, 16 b, and 16 c are formed on the principal surfaceof the mounting substrate 10, but these may equally be formed on alateral surface of the mounting substrate 10. Alternatively,interconnects may be formed on the surface opposite to the principalsurface of the mounting substrate 10 (the rear surface), and may beelectrically connected to the principal surface through through holes orthe like formed in the mounting substrate 10. Instead, the interconnectsmay be formed on any two or all of the principal surface, a lateralsurface and the rear surface of the mounting substrate 10. It should benoted that the largest surface of the mounting substrate 10 is commonlythe principal surface, but even if not the largest surface, the surfaceon which it is possible to mount the optical element is the principalsurface.

A semiconductor chip 20 is electrically connected by the flip-chipbonding to the interconnects 16 a and 16 c. That is to say, metal bumpsare formed on the electrodes of the semiconductor chip 20, and thesemiconductor chip 20 is connected to the mounting substrate 10 formingthe interconnect substrate by the face-down bonding. The semiconductorchip 20 has a CMOS circuit, for example. The interconnect 16 c forms anelectrical input/output terminal. In this embodiment, one semiconductorchip 20 is fitted, but a plurality of semiconductor chips 20 may befitted. For example, a plurality of semiconductor chips 20 may be fittedcorresponding to a plurality of optical elements.

A surface-emission laser 22 is electrically connected to an interconnect16 b by the flip-chip bonding. On one surface of the surface-emissionlaser 22 is formed an electrode 24 on the other surface are formedelectrodes 26 and a light-emitting aperture 28. The surface-emissionlaser 22 is disposed on the principal surface of the mounting substrate10 so that light emitted from the aperture 28 is reflected by the endportion 18, to pass along the core 12. The electrodes 26 andinterconnect 16 b are electrically connected. The emitting aperture 28and electrodes 26 are sealed with a transparent resin 34 having lighttransmitting characteristics. The transparent resin 34 is a siliconeresin having light transmitting characteristics. The electrode 24 iselectrically connected to the interconnect 16 a by a wire 30. In thisembodiment, a plurality of surface-emission lasers 22 are provided as anexample of a plurality of optical elements, but the present invention isnot limited to this. For example, a single optical element may beprovided, and this optical element may have a plurality oflight-admitting apertures or light-emitting apertures. Naturally, asingle optical element with a single light-admitting aperture orlight-emitting aperture may also be provided.

The semiconductor chip 20 and surface-emission laser 22 are sealed witha resin 36 having light blocking characteristics. However, the resin 36is provided in such a way as not to impede the passage of light betweenthe optical element (for example, the surface-emission laser 22) and theoptical waveguide (for example the core 12). The resin 36 is an epoxyresin. The components of the epoxy resin are from 10 to 50 per centepoxy and from 90 to 50 per cent filler (silica or the like). In thisembodiment, three optical waveguides are aligned in parallel. That is tosay, the three cores 12 forming the three optical waveguides are formedwithin the mounting substrate 10. Moreover, the three cores 12 (opticalwaveguides) are disposed in parallel, and the optical output terminal 29of each of their cores 12 (optical waveguides) are formed on the samelateral surface of the mounting substrate 10. The three surface-emissionlasers 22 connected to the optical waveguides are mounted on themounting substrate 10 at the end distant from the optical outputterminals 29.

Operation

Electrical signals from the semiconductor chip 20 are transferred to thesurface-emission laser 22. By this means, the surface-emission laser 22emits light 32. The light 32 is emitted from the emitting aperture 28,and at the end portion 18 of the optical waveguide is reflected through90 degrees. Then it proceeds along the center of the core 12 in thedirection of the arrow, and is transmitted through the optical outputterminal 29 to an optical fiber or the like.

Effect

In this embodiment, the mounting substrate 10 doubles as an opticalwaveguide. Therefore, the optical module can be made thinner. As aresult, the optical module can be made more compact and lightweight.

In this embodiment, when aligning the optical waveguide andsurface-emission laser 22, there are two items involved in thepositioning: the mounting substrate 10 (optical waveguide) and thesurface-emission laser 22. Thus the bonding of the surface-emissionlaser and the optical waveguide which conventionally was complicated andtime-consuming is simplified, and the bonding strength can also beimproved. Additionally, the costs associated with bonding can bereduced.

Other matters

In this embodiment, the direction of the light is changed by a 45-degreemirror. However, this is not limitative of the invention, and this anyother component appropriate for changing the direction of the light maybe applied in the invention.

In this embodiment, the direction of the light is changed at the endportion of the waveguide. However, this is not limitative of theinvention, and the direction of the light may be changed at a portionother than the end portion of the waveguide.

In this embodiment, the surface-emission laser 22 must inject light intothe optical waveguide, and therefore the mounting position of thesurface-emission laser 22 is restricted. However, the semiconductor chip20 can be mounted anywhere as long as it is on the principal surface ofthe mounting substrate 10.

In this embodiment, the surface-emission laser 22 and semiconductor chip20 are mounted on the mounting substrate 10 by the flip-chip bonding.However, this is not limitative of the invention, and thesurface-emission laser 22 or semiconductor chip 20 may equally bemounted by face-up bonding or the like.

In this embodiment, the semiconductor chip 20 is mounted on the mountingsubstrate 10. However, this is not limitative of the invention, and onthe principal surface of the mounting substrate 10 may be formed acircuit of thin-film transistors, which may be used in place of thesemiconductor chip 20. Alternatively, with such a thin-film transistorcircuit and the semiconductor chip 20 may be formed a circuit to sendsignals to the surface-emission laser 22.

In this embodiment, the mounting substrate 10 is made of glass. However,this is not limitative of the invention, and a polymer or suchlike filmmay be used for the mounting substrate 10.

In this embodiment, the surface-emission laser 22 constitutes an opticalelement. However, this is not limitative of the invention, and a laserdiode, photodiode, or other optical element may equally be used.

What is claimed is:
 1. An optical module comprising: a mounting memberhaving a principal surface, said mounting member entirely made of glassand having a core and a cladding formed therein, said cladding havingits surface to form said principal surface in whole; an interconnectformed on said mounting member; an optical element mounted on saidprincipal surface and electrically connected to said interconnect; and asemiconductor element driving said optical element, said semiconductorelement mounted on said principal surface, wherein said mounting memberis an optical waveguide for guiding light emitted from said opticalelement or light admitted to said optical element.
 2. The optical moduleas defined in claim 1, wherein a light-admitting aperture orlight-emitting aperture of said optical element is disposed opposingsaid principal surface.
 3. The optical module as defined in claim 2,wherein a light-reflecting member is provided on said optical waveguide;and wherein light is transmitted between said optical element and saidoptical waveguide through said light-reflecting member.
 4. An opticalmodule comprising: an optical element for emitting or admitting light;an optical waveguide entirely made of glass, having a core and acladding formed therein and having a principal surface, with saidoptical element mounted on said principal surface, for guiding lightemitted from said optical element or light admitted to said opticalelement, said cladding having its surface to form said principal surfacein whole; and a semiconductor element driving said optical element, saidsemiconductor element mounted on said principal surface.
 5. The opticalmodule as defined in claim 4, wherein said optical element and saidoptical waveguide are fixed with an adhesive member having lighttransmitting characteristics interposed between said optical element andsaid optical waveguide in such a way that the position of emission oradmission of light of said optical element opposes said opticalwaveguide, and are subjected to bare chip mounting.
 6. The opticalmodule as defined in claim 5, wherein said optical waveguide has amodifying portion whereby the direction of progress of said light ischanged; and wherein said optical element is positioned to overlie saidmodifying portion.
 7. The optical module as defined in claim 4, whereinsaid optical element and said semiconductor element are integrallysealed with a resin.
 8. The optical module as defined in claim 5,wherein said optical element and said semiconductor element areintegrally sealed with a resin.
 9. The optical module as defined inclaim 6, wherein said optical element and said semiconductor element areintegrally sealed with a resin.
 10. The optical module as defined inclaim 7, wherein said resin has light blocking characteristics.
 11. Theoptical module as defined in claim 8, wherein said resin has lightblocking characteristics.
 12. The optical module as defined in claim 9,wherein said resin has light blocking characteristics.
 13. The opticalmodule as defined in claim 4, wherein a circuit is laminated directly onsaid principal surface.
 14. An optical module comprising: an opticalelement; a mounting member, said mounting member entirely made of glassand having a core and a cladding formed therein to have a function of anoptical waveguide for guiding light emitted from said optical element orlight admitted to said optical element, said mounting memberelectrically connected to said optical element or a semiconductorelement associated with said optical element, said mounting memberhaving a principal surface, said cladding having its surface to formsaid principal surface in whole; and a semiconductor element drivingsaid optical element, said semiconductor element mounted on saidprincipal surface.
 15. An optical module comprising: a mounting memberhaving a principal surface and a lateral surface, said mounting memberentirely made of glass and having a core and a cladding formed therein,said cladding having its surface to form said principal surface inwhole; an optical element mounted on said principal surface; and asemiconductor element driving said optical element, said semiconductorelement mounted on said principal surface, wherein said mounting memberhas a function of an optical waveguide, and an optical input/outputterminal for said optical waveguide is provided on said lateral surface.